A data carrier according to the design described in the first paragraph above and a circuit according to the design described in the second paragraph above are disclosed, for example, in the patent document WO 99/65168 A2. The known data carrier with the known circuit has a design in which the processing means for processing the response signal are formed in a plurality of different time windows and in which that time window in which the known data carrier generates its transmission signal formed from the response signal and transmits it to a communication station is determined as a function of a portion of the serial number significant for this data carrier.
With regard to a data carrier in which the processing means are designed to process a response signal in a plurality of time windows, reference may also be made to the patent document U.S. Pat. No. 5,539,394 A, which in the aforementioned patent document WO 99/65168 A2 is acknowledged as the state of the art. In the data carriers disclosed by the two patent documents WO 99/65168 A2 and U.S. Pat. No. 5,539,394 A cited above, processing means are provided in which the onset point of time windows during which the transmission signal to be transmitted from the data carrier to the communication station can be transmitted to a communication station is selected as a variable transmission parameter.
However, a subcarrier signal may also be selected as the variable transmission parameter, the relevant data carrier then being designed to generate different subcarrier signals and preferably to generate subcarrier signals differing in respect of their subcarrier frequency, and the subcarrier signals differing in respect of their subcarrier frequency being used for the modulation of a response signal for the purpose of generating a transmission signal suitable for transmission to a communication station. Reference may be made, in this context, to the patent document U.S. Pat. No. 5,485,154 A.
Common to all the known data carriers mentioned above is the fact that the generation of response signals and hence of transmission signals is dependent only on portions of a serial number or of random numbers or of other memory contents stored in a memory of the known data carrier. In the case of the known data carriers, this means that, with a plurality of data carriers present in a communication range of a communication station, it can happen relatively frequently that two data carriers transmit their transmission signal to a communication station using the same transmission parameters, for example using the same time window, one of two such data carriers possibly being situated relatively close to a communication station and the other data carrier relatively far away from the communication station, and the problem then arising that the data carrier situated relatively close to the communication station transmits a relatively strong transmission signal to the communication station, whereas the data carrier situated relatively far away from the communication station transmits only a relatively weak transmission signal to the communication station, which may and unfortunately often does mean that the transmission signal of the data carrier situated relatively close to the communication station masks the transmission signal of the data carrier situated relatively far away from the communication station, so that the data carrier situated relatively far away from the communication station is then not detected by the communication station and cannot be further processed, for example selected, read out, or written to when the need subsequently arises. This state of affairs may lead to a failure situation or give rise to high costs, incurred in detecting all data carriers situated in a communication range of a communication station in order to avoid such a failure situation.